Manufacture of cuprammonium rayon



' June 29,1943. w. FURNESS 2,322,801

MANUFACTURE OF U PRAMMONIUM RAYON Filed May 1', 1940 DRYING ACID I WASH WATER WASH K Ill '2 z l I I b I I I .1 I q I I I i g m l I INVENTOR:

ATTORNEYS.

Patented June 29,1943

MANUFACTURE OF CUPRAIWMONIUM RAYON William H. Furness, Haddonileld, N. 1., assignor to American Rayon Company, Inc., Riverton, N. J a corporation of New Jersey Application May 1, 1940, Serial No. 332,696

2 Claims.

This invention relates t the art of manufacturing cuprammonium rayon and other cellulose products from cuprammonium cellulosic solutions, and its nature, objects and advantages will be best understood from the following.

Generally speaking, in the spinning of cuprammonium rayon, for example, the cellulosic spinning solution is prepared and spun through suitable spinnerets into a caustic soda setting bath, and the bundle of filaments, after leaving the setting bath and while in a plastic state, is subjected to a sulphuric acid wash for the purpose of removing caustic soda, copper and ammonia from the filaments. It is latersubjected to water washing to remove acid and soluble salts, and then to a drying operation.

This general procedure has several drawbacks. One of these is the difficulty and expense of recovery of chemicals. For example, the caustic soda, during the process, is converted into sodium sulphate, and the solutions are so dilute and the expense of recovering the sodium sulphate is so great that the solution is discarded. The case is the same with the ammonia, which is converted into ammonium sulphate during the process. With respect to the copper, the usual practice has been to recover it by the addition of caustic soda to form basic copper sulphate, and here again sodium sulphate is formed and the solution of sodium sulphate is so dilute that it is discarded, with the resultant loss in caustic soda consumed to form the sodium sulphate. Another difficulty is that relatively large quan-! titles of sulphuric acid. are required.

The primary object of the present invention is to overcome these diiliculties and to make it possible to recover for're-use, the caustic soda, copper and amm0nla,-- in a very simple and effective manner.

In carrying out my invention I prefer to, employ the cellulosic spinning solution from wood pulp, according to my copending application Serial No. 129.820, filed March 9. 1937 (now Patent No. 2,225,431, dated December 1'7. 1940). Briefly, the wood pulp is firsii subjected to caustic soda solution to eii'ect'certain changes therein, after which surplus caustic soda solution, is expressed and the treated wood pulp, together with ammonia and tetrammonio cop-- per sulphate are used to prepare the spinning solution. For this spinning solution, the caustic soda employed should be in the ratio of 2 mols for each mol of copper sulphate, and the ammonia should be in'the ratio of from about '1 to about 8 mols, although the quantity employed may be greater.

This solution is spun into a caustic, soda setting bath which is relatively dilute, containing from about 25 to 45 grams per liter to remove practically all of the ammonia, the

bulk of the caustic soda, and a substantial portion of the copper, for reasons which will 'hereafter appear. In order to accomplish this, I operate on a continuous basis, as diagrammatically illustrated in the accompanying drawing wherein the reference character A denotes a sourceof cellulosic spinning solutiomwhich is pumped through spinnerets B into the caustic soda setting bath C, from which the bundle of filaments, through the use of suitable guides, not shown, is led to a revolving cage D, which operates to continuously advance the bundle of filaments in the form of a helix. In the order named, the helix is subjected to a hot water wash, then to the sulphuric acid wash, then to a water wash, and finally to a drying operation carried out, if desired, on the cage. For convenience in separation of the treatment or wash liquids and for other reasons, the bundle of filaments, after leaving the hot water wash section, is led from the case over a roller E and then back to the cage, from which point it is advanced in the form of a helix as before.

The hot water wash has the efl'ect of removing the bulk of the caustic soda, practically all of the ammonia and a substantial part of the copper from the filaments. Although the water need not be hot, I prefer hot water for the reason that caustic soda is more soluble in hot water than in cold and further, it is desirable to use no more water than will accomplish the desired end, and the results can be obtained with a smaller volume of water, if hot. The water dilutes the ammonia in and on the filaments, thus tending to cause cupric hydroxide 1 resulting from the action of the caustic soda of the setting bath) to come out of solution, and the continual application of the water physically removes ammonia and copper hydroxide. Moreover, the heat drives oi! some of the ammon a as gas, thus further decreasing the concentration of ammonia and increasing the tendency of the copper to come out of solution. The copper hydroxide is given an opportunity to settle out soluble basic copper sulphate which by the water, for all practical purposes all .of the ammoniais removed from the filaments. which is important for reasons hereinafter ape pearing.

The advantages of removing the bulk or the caustic soda before the filaments are subjected to the sulphuric acid wash, are as follows. In

the-first place, since caustic soda is used in the setting bath, it is highly desirable'from the standpoint of eifectiveness, to recover the' caustic soda, as such, so that it, can be returned to the spinning bath. .This can not be effectively done if the caustic soda is removed in the acid section, because as a result of the reactions occurring in that section, the caustic sodais consumed in forming sodium sulphate, and the cost of recovering it is so expensive as to be prohibitive. I can readily make the caustic soda in the 'hot water wash liquor available for re-use in the system by boiling it to drive oil the ammonia therein and, if needed, to drive oil sumcient water to increase the concentration of. caustic soda to the point where the concentrated liquor can be returned to the setting bath storage tank. In theif desired, removed as set forth in my copending.

application, Serial No. 332,694, filed May 1, 1940.

The advantages of removing a substantial part of the copper from the filaments in the hot water wash ection are as follows. Less acid is required,- for there is less copper to remove. Moreover, an

excess of sulphuric acid over'the theoretical requirements is always needed in the acid wash section for obvious reasons, and consequently the acid wash liquor always contains some free acid, in addition to the sodium sulphate and the copper sulphate produced as a result of the reactions occurring in the acid wash section. Now, I propose to recover the copper sulphate in the acid wash liquor by adding cupric hydroxide which converts the soluble copper sulphate into the in- I can be separated as by sedimentation, centrifuging, filtering or the like. By removing copper from the filaments in the hot water wash section, in the form of cupric hydroxide, I have thus available cupric hydroxide for use in neutralizing the excess sulphur'ic acid in the acid wash liquor, the reaction between the sulphuric acid and the cupric hydroxide being to form some copper sulphate,

which, in addition to the copper sulphate already present in the wash liquor, is recovered, as above set forth, by the addition of the acid wash liquors of further amounts of cupric hydroxide suiflcient to convert all of the copper sulphate into basic the ammonia from the filaments in ,thehot water wash section are as follows. As before, this less-' ens the amount of acid required. In the next place. the presence of substantial ammonia in the filaments reaching the acid wash section would result in the formation in that section of ammonium sulphate which would be present inthe acid wash liquor. This would interfere with the removal of copper sulphate from the acid wash liquor in the form of basic copper sulphate, by the use of cupric hydroxide. By the hot water wash .the ammonia in thefllaments, if not entirely removed, is reduced to such a small amount as not to interfere with the removal of the copper sulphate as basic copper sulphate. Furthermore, ammonia is needed to convert the basic copper sulphate into tetramm'onio copper sulphate, and the ammonia removed by the hot water washing operation is very easily recoverable as ammonia water and is used as a source of ammonia for the conversion of basic copper sulphate into tetrammonio copper sulphate. The products of the reaction between basic copper sulphate and ammonia are tetrammonio copper sulphate and cu-.

pric hydroxide, the latter being separated in any ofthe ways described. The tetrammonio copper sulphate is used in the manufacture of the cellulosic spinning solution, and the copper hydroxide obtained by the reaction between basic copper sulphate and ammonia, is available for removing copper sulphate from; the acid wash liquor.

Another advantage of removing ammonia from the filaments and recovering the same from the wash liquors for re-use as indicated is that thereby the final supematant liquors are freed of ammonia. These final supernatant liquorsare ulti-. mately re-used in the system by returning them to the spinning bath system. This is of advan- 4 tage because ammonia in the setting bath intercupric oxide.

copper sulphate. I prefer to remove at least sufacid wash liquor to convert copper sulphate into a basic copper sulphate.

The advantages of removing practically all of feres with good spinning. In this connection I employ a relatively dilute caustic soda setting bath which is more effective for spinning, the less the ammonia present therein.

There are traces of chemicals in the water wash section following the acid wash, but-the amount is o small as to be negligible.

Instead of using a single case, two cages may be used, the first cage constituting thehot water wash section, and the second cage the acid section, followed by water washing and drying. It is also obvious that the principles of the invem tion can be carried out with other'apparatus.

' The water in the hot water wash section should be hot enough to effectively remove the bulk of the caustic soda ,and preferably not so hot as to convert the copper hydroxide to the black uneconomical, since the copper hydroxide can be used as such.

It is of course obvious that the length of the hot water section should be such that ample opportunity is provided for the filaments to be subjected to the hot water wash 'sufllciently long to accomplish the desired removalof caustic soda, ammonia and copper. The period will vary with the variation in denier of the filaments; Likewise the acid wash section should be long enough I to serve the functions for which th acid i g ployed.

Thecomplete system by which I manufacture cuprammonium rayon and recover chemicals, etc..

is described and claimed in, my copending appli-' cation Serial No. 332,694, filed Mayl, 1940. Thatsystem advantageously employs the present/ invention but since the present invention is capable To use water that hot would be of independent use, I herein claim it apart from 'the general system.

What I claim is:

1. In a continuous system of spinning and treating cellulosic products such as rayon, staple, nlms and the like, from cuprammonium cellulosic solutions, in which the filaments, films or the like, are spun into a caustic sodarsettlng bath and afterwards subjected to a sulphuric acid wash. the process which comprises subjecting the freshly spun material intermediate the setting bath and the acid washan'd while in a plastic state to a hotwater wash to remove substantially all of the caustic soda and the ammonia,'and a substantial portion of the copper as cupric hydroxide. separating the cupric hydroxide and washing it, and usingthe washed cupric hydroxide to remove acid intheused wash 11110011.

; 2. In a continuous system of spinning and treating cellulosic products such as rayon, staple,

iilms and the like, from cuprammonium cellulosic solutions, in which the filaments, films, or

the like are spun into a caustic soda setting bath 01' the copper as cuprie hydroxide, separating the cupric hydroxide and washing it, and using the washed cupric hydroxide to remove free acid and copper sulphate in the used wash liquors, thereby producing basic copper sulphate for use in making fresh spinning solutions.

* WILLIAM H. FURNESS. 

